A novel, highly sensitive and specific biomarker for Niemann-Pick type C1 disease

Expanded access with intravenous hydroxypropyl-β-cyclodextrin to treat children and young adults with Niemann-Pick disease type C1: a case report analysis

Background

Niemann-Pick Disease Type C (NPC) is an inherited, often fatal neurovisceral lysosomal storage disease characterized by cholesterol accumulation in every cell with few known treatments. Defects in cholesterol transport cause sequestration of unesterified cholesterol within the endolysosomal system. The discovery that systemic administration of hydroxypropyl-beta cyclodextrin (HPβPD) to NPC mice could release trapped cholesterol from lysosomes, normalize cholesterol levels in the liver, and prolong life, led to expanded access use in NPC patients. HPβCD has been administered to NPC patients with approved INDs globally since 2009.

Results

Here we present safety, tolerability and efficacy data from 12 patients treated intravenously (IV) for over 7 years with HPβCD in the US and Brazil. Some patients subsequently received intrathecal (IT) treatment with HPβCD following on average 13 months of IV HPβCD. Several patients transitioned to an alternate HPβCD. Moderately affected NPC patients treated with HPβCD showed slowing of disease progression. Severely affected patients demonstrated periods of stability but eventually showed progression of disease. Neurologic and neurocognitive benefits were seen in most patients with IV alone, independent of the addition of IT administration. Physicians and caregivers reported improvements in quality of life for the patients on IV therapy. There were no safety issues, and the drug was well tolerated and easy to administer.

Conclusions

These expanded access data support the safety and potential benefit of systemic IV administration of HPβCD and provide a platform for two clinical trials to study the effect of intravenous administration of HPβCD in NPC patients.

Determination of the Pathological Features of NPC1 Variants in a Cellular Complementation Test

Niemann-Pick Type C (NP-C) is a rare disorder of lipid metabolism caused by mutations within the NPC1 and NPC2 genes. NP-C is a neurovisceral disease leading to a heterogeneous, multisystemic spectrum of symptoms in those affected. Until now, there is no investigative tool to demonstrate the significance of single variants within the NPC genes. Hence, the aim of the study was to establish a test that allows for an objective assessment of the pathological potential of NPC1 gene variants. Chinese hamster ovary cells defective in the NPC1 gene accumulate cholesterol in lysosomal storage organelles. The cells were transfected with NPC1-GFP plasmid vectors carrying distinct sequence variants. Filipin staining was used to test for complementation of the phenotype. The known variant p.Ile1061Thr showed a significantly impaired cholesterol clearance after 12 and 24 h compared to the wild type. Among the investigated variants, p.Ser954Leu and p.Glu1273Lys showed decelerated cholesterol clearance as well. The remaining variants p.Gln60His, p.Val494Met, and p.Ile787Val showed a cholesterol clearance indistinguishable from wild type. Further, p.Ile1061Thr acquired an enhanced clearance ability upon 25-hydroxycholesterol treatment. We conclude that the variants that caused an abnormal clearance phenotype are highly likely to be of clinical relevance. Moreover, we present a system that can be utilized to screen for new drugs.

Structural Determination of Lysosphingomyelin-509 and Discovery of Novel Class Lipids from Patients with Niemann-Pick Disease Type C

Niemann-Pick disease type C (NPC) is an autosomal recessive disorder caused by the mutation of cholesterol-transporting proteins. In addition, early treatment is important for good prognosis of this disease because of the progressive neurodegeneration. However, the diagnosis of this disease is difficult due to a variety of clinical spectrum. Lysosphingomyelin-509, which is one of the most useful biomarkers for NPC, was applied for the rapid and easy detection of NPC. The fact that its chemical structure was unknown until recently implicates the unrevealed pathophysiology and molecular mechanisms of NPC. In this study, we aimed to elucidate the structure of lysosphingomyelin-509 by various mass spectrometric techniques. As our identification strategy, we adopted analytical and organic chemistry approaches to the serum of patients with NPC. Chemical derivatization and hydrogen abstraction dissociation-tandem mass spectrometry were used for the determination of function groups and partial structure, respectively. As a result, we revealed the exact structure of lysosphingomyelin-509 as N-acylated and O-phosphocholine adducted serine. Additionally, we found that a group of metabolites with N-acyl groups were increased considerably in the serum/plasma of patients with NPC as compared to that of other groups using targeted lipidomics analysis. Our techniques were useful for the identification of lysosphingomyelin-509.

Investigation of diagnostic performance of five urinary cholesterol metabolites for Niemann-Pick disease type C

Niemann-Pick disease type C (NPC) is an autosomal recessive disorder characterized by progressive nervous degeneration. Because of the diversity of clinical symptoms and onset age, the diagnosis of this disease is difficult. Therefore, biomarker tests have attracted significant attention for earlier diagnostics. In this study, we developed a simultaneous analysis method for five urinary conjugated cholesterol metabolites, which are potential diagnostic biomarkers for a rapid, convenient, and noninvasive chemical diagnosis, using LC/MS/MS. By the method, their urinary concentrations were quantified and the NPC diagnostic performances were evaluated. The developed LC/MS/MS method showed high accuracy and satisfied all analytical method validation criteria. When the urine of healthy controls and patients with NPC was analyzed, three of five urinary conjugated cholesterol metabolite concentrations corrected by urinary creatinine were significantly higher in the patients with NPC. As a result of receiver operating characteristics analysis, these urinary metabolites might have excellent diagnostic marker performance. 3β-Sulfooxy-7β-hydroxy-5-cholenoic acid showed particularly excellent diagnostic performance with both 100% clinical sensitivity and specificity, suggesting that it is a useful NPC diagnostic marker. The urinary conjugated cholesterol metabolites exhibited high NPC diagnostic marker performance and could be used for NPC diagnosis.

Laboratory diagnosis of the Niemann-Pick type C disease: an inherited neurodegenerative disorder of cholesterol metabolism

Niemann-Pick type C disease (NPC) is a genetically determined neurodegenerative metabolic disease resulting from the mutations in the NPC1 or NPC2 genes. It belongs to the lysosomal storage diseases and its main cause is impaired cholesterol transport in late endosomes or lysosomes. NPC is inherited in an autosomal recessive trait. Due to the wide range in age of onset, often unspecific clinical picture and varying dynamics of disease progression, the diagnosis is very difficult and long-lasting. The most characteristic visceral symptoms are hepato- or hepatosplenomegaly, which may appear independently of neurological or psychiatric symptoms at various stages of the disease. Available biochemical biomarkers should be tested as early as possible in patients presenting with hepato- or hepatosplenomegaly, long-lasting cholestatic jaundice in neonates or infantile patients, as well as in individuals at any age with: vertical supranuclear gaze palsy (VSGP), ataxia, dystonia, frontotemporal dementia and untreatable schizophrenia or psychosis. Research on biomarkers which can detect NPC patients (Cholestan-3β, 5α, 6β-triol, 7-ketocholesterol, lysosphingomyelin isoforms and bile acid metabolites) is still ongoing, although they are not specific for the NPC disease only. This mini review describes currently used diagnostic methods.

N-acyl-O-phosphocholineserines: structures of a novel class of lipids that are biomarkers for Niemann-Pick C1 disease

Niemann-Pick disease type C1 (NPC1) is a fatal, neurodegenerative, cholesterol storage disorder. With new therapeutics in clinical trials, there is an urgency to improve diagnostics and monitor therapeutic efficacy with biomarkers. In this study, we sought to define the structure of an unknown lipid biomarker for NPC1 with [M + H]⁺ ion at m/z 509.3351, previously designated as lysoSM-509. The structure of N-palmitoyl-O-phosphocholineserine (PPCS) was proposed for the lipid biomarker based on the results from mass spectrometric analyses and chemical derivatizations. As no commercial standard is available, authentic PPCS was chemically synthesized, and the structure was confirmed by comparison of endogenous and synthetic compounds as well as their derivatives using liquid chromatography-tandem mass spectrometry (LC-MS/MS). PPCS is the most abundant species among N-acyl-O-phosphocholineserines (APCS), a class of lipids that have not been previously detected in biological samples. Further analysis demonstrated that all APCS species with acyl groups ranging from C14 to C24 were elevated in NPC1 plasma. PPCS is also elevated in both central and peripheral tissues of the NPC1 cat model. Identification of APCS structures provide an opportunity for broader exploration of the roles of these novel lipids in NPC1 disease pathology and diagnosis.

Plasma and dried blood spot lysosphingolipids for the diagnosis of different sphingolipidoses: a comparative study

Background

Lysosphingolipids, the N-deacylated forms of sphingolipids, have been identified as potential biomarkers of several sphingolipidoses, such as Gaucher, Fabry, Krabbe and Niemann-Pick diseases and in GM1 and GM2 gangliosidoses. To date, different methods have been developed to measure various lysosphingolipids (LysoSLs) in plasma. Here, we present a novel liquid chromatography tandem mass spectrometry (LC-MS/MS) assay for a simultaneous quantification of LysoSLs (HexSph, LysoGb3, LysoGM1, LysoGM2, LysoSM and LysoSM509) in dried blood spot (DBS). This LC-MS/MS method was used to compare the levels of LysoSLs in DBS and plasma in both affected patients and healthy controls.

Methods

Lysosphingolipids were extracted from a 3.2 mm diameter DBS with a mixture of methanol:acetonitrile:water (80:15:5, v/v) containing internal stable isotope standards. Chromatographic separation was performed using a C18 column with a gradient of water and acetonitrile both with 0.1% formic acid in a total run time of 4 min. The compounds were detected in the positive ion mode electrospray ionization (ESI)-MS/MS by multiple reaction monitoring (MRM).

Results

The method was validated on DBS to demonstrate specificity, linearity, lowest limit of quantification, accuracy and precision. The reference ranges were determined in pediatric and adult populations. The elevated levels of LysoSLs were identified in Gaucher disease (HexSph), Fabry disease (LysoGb3), prosaposin deficiency (HexSph and LysoGb3) and Niemann-Pick disease types A/B and C (LysoSM and LysoSM509). The correlation in the levels between DBS and plasma was excellent for LysoGb3 and HexSph but poor for LysoSM and LysoSM509.

Conclusions

Despite the fact that plasma LysoSLs determination remains the gold standard, our LC-MS/MS method allows a rapid and reliable quantification of lysosphingolipids in DBS. The method is a useful tool for the diagnosis of different sphingolipidoses except for Niemann-Pick type C.

Lysosomal diseases: Overview on current diagnosis and treatment

Lysosomal diseases (LDs), also known as lysosomal storage diseases (LSDs), are a heterogeneous group of conditions caused by defects in lysosomal function. LDs may result from deficiency of lysosomal hydrolases, membrane-associated transporters or other non-enzymatic proteins. Interest in the LD field is growing each year, as more conditions are, or will soon be treatable. In this article, we review the diagnosis of LDs, from clinical suspicion and screening tests to the identification of enzyme or protein deficiencies and molecular genetic diagnosis. We also cover the treatment approaches that are currently available or in development, including hematopoietic stem cell transplantation, enzyme replacement therapy, small molecules, and gene therapy.

Psychiatric and neurological symptoms in patients with Niemann-Pick disease type C (NP-C): Findings from the International NPC Registry

Objectives: Niemann-Pick disease type C (NP-C) is a rare inherited neurovisceral disease that should be recognised by psychiatrists as a possible underlying cause of psychiatric abnormalities. This study describes NP-C patients who had psychiatric manifestations at enrolment in the international NPC Registry, a unique multicentre, prospective, observational disease registry. Methods: Treating physicians' data entries describing psychiatric manifestations in NPC patients were coded and grouped by expert psychiatrists. Results: Out of 386 NP-C patients included in the registry as of October 2015, psychiatric abnormalities were reported to be present in 34% (94/280) of those with available data. Forty-four patients were confirmed to have identifiable psychiatric manifestations, with text describing these psychiatric manifestations. In these 44 patients, the median (range) age at onset of psychiatric manifestations was 17.9 years (2.5-67.9; n = 15), while the median (range) age at NP-C diagnosis was 23.7 years (0.2-69.8; n = 34). Almost all patients (43/44; 98%) had an occurrence of ≥1 neurological manifestation at enrolment. Conclusions: These data show that substantial delays in diagnosis of NP-C are long among patients with psychiatric symptoms and, moreover, patients presenting with psychiatric features and at least one of cognitive impairment, neurological manifestations, and/or visceral symptoms should be screened for NP-C.

Systematic review of psychiatric signs in Niemann-Pick disease type C

Objectives: We conducted the first systematic literature review and analysis of psychiatric manifestations in Niemann-Pick disease type C (NPC) to describe: (1) time of occurrence of psychiatric manifestations relative to other disease manifestations; and (2) frequent combinations of psychiatric, neurological and visceral disease manifestations. Methods: A systematic EMBase literature search was conducted to identify, collate and analyze published data from patients with NPC associated with psychiatric symptoms, published between January 1967 and November 2015. Results: Of 152 identified publications 40 were included after screening that contained useable data from 58 NPC patients (mean [SD] age at diagnosis of NPC 27.8 [15.1] years). Among patients with available data, cognitive, memory and instrumental impairments were most frequent (90% of patients), followed by psychosis (62%), altered behavior (52%) and mood disorders (38%). Psychiatric manifestations were reported before or at neurological disease onset in 41 (76%) patients; organic signs (e.g., hepatosplenomegaly, hearing problems) were reported before psychiatric manifestations in 12 (22%). Substantial delays to diagnosis were observed (5-6 years between psychiatric presentation and NPC diagnosis). Conclusions: NPC should be considered as a possible cause of psychiatric manifestations in patients with an atypical disease course, acute-onset psychosis, treatment failure, and/or certain combinations of psychiatric/neurological/visceral symptoms.

Animal models for Niemann-Pick type C: implications for drug discovery & development

INTRODUCTION

Niemann-Pick type C (NPC) is a neurovisceral, progressively detrimental lysosomal storage disease with very limited therapeutic options and no approved treatment available in the US. Despite its rarity, NPC has seen increased drug developmental efforts over the past decade, culminating in the completion of two potential registration trials in 2018. Areas covered: This review highlights the many available animal models that have been developed in the field and briefly covers classical and new cell technologies. This review provides a high-level evaluation and prioritization of the various models with regard to efficient and clinically translatable drug development, and briefly discusses the relevant developments and opportunities pertaining to this. Expert opinion: With a number of in vitro and in vivo models available, and with having several drugs, all with various mechanisms of action, either approved or in late stage development, the NPC field is in an exciting time. One of the challenges for researchers and developers will be the ability to make use of the lessons learnt from existing late-stage programs as well as the incorporation not only of the opportunities but also the limitations of the many models into successful drug discovery and translational development programs.

Diagnostic performance evaluation of sulfate-conjugated cholesterol metabolites as urinary biomarkers of Niemann-Pick disease type C

BACKGROUND

Niemann-Pick disease type C (NPC) is an autosomal recessive inherited disorder with progressive neuronal degeneration. Because conventional diagnostic methods are complicated and invasive, biomarker tests have drawn attention. We aimed to evaluate three urinary conjugated cholesterol metabolites as diagnostic biomarkers for NPC.

METHODS

Urine samples from 23 patients with NPC, 28 healthy controls, and 7 patients with inherited metabolic disorders were analyzed. 3β-Sulfooxy-7β-N-acetylglucosaminyl-5-cholen-24-oic acid and its glycine and taurine conjugates in urine were quantified by liquid chromatography-tandem mass spectrometry. The diagnostic performance of the three metabolites and their total concentration was evaluated.

RESULT

Creatinine-corrected concentrations of three metabolites and their total concentration were all significantly higher in NPC patients (0.0098 < P < .0448). The area under the receiver operating curve for all metabolites exceeded 0.95, the clinical specificity was 92-100%, and the clinical sensitivity was ~95%. In the urine of patients with other inherited metabolic diseases, the concentrations of the metabolites were lower than those in the urine of patients with NPC.

CONCLUSION

These conjugated cholesterol metabolites in urine can serve as useful diagnostic markers for noninvasive screening of NPC.

Chronic visceral acid sphingomyelinase deficiency (Niemann-Pick disease type B) in 16 Polish patients: long-term follow-up

BACKGROUND

Acid sphingomyelinase deficiency (ASMD), due to mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene, is divided into infantile neurovisceral ASMD (Niemann-Pick type A), chronic neurovisceral ASMD (intermediate form, Niemann-Pick type A/B) and chronic visceral ASMD (Niemann-Pick type B). We conducted a long-term observational, single-center study including 16 patients with chronic visceral ASMD.

RESULTS

12 patients were diagnosed in childhood and 4 others in adulthood, the oldest at the age of 50. The mean time of follow-up was approximately 10 years (range: 6 months - 36 years). Splenomegaly was noted in all patients at diagnosis. Hepatomegaly was observed in 88% of patients. Moderately elevated (several-fold above the upper limit of normal values) serum transaminases were noted in 38% of patients. Cherry-red spots were found in five Gypsy children from one family and also in one adult Polish patient, a heterozygote for p.delR610 mutation. Dyslipidemia was noted in 50% of patients. Interstitial lung disease was diagnosed in 44% of patients. Plasmatic lysosphingomyelin (SPC) was elevated in all the patients except one with p.V36A homozygosity and a very mild phenotype also presenting with elevated plasmatic SPC-509 but normal chitotriosidase activity. The most common variant of SMPD1 gene was p.G166R. We found a previously unreported variant in exon 2 (c.491G > T, p.G164 V) in one patient.

CONCLUSIONS

Chronic visceral ASMD could constitute a slowly progressing disease with a relatively good outcome. The combined measurement of lysosphingomyelin (SPC) and lysospingomyelin-509 (SPC-509) is an essential method for the assessment of ASMD course.

Diagnosis of niemann-pick C1 by measurement of bile acid biomarkers in archived newborn dried blood spots

BACKGROUND

Niemann-Pick disease type C1 (NPC1) is a rare, neurodegenerative cholesterol storage disorder. Diagnostic delay of >5 years is common due to the rarity of the disease and non-specific early symptoms. To improve diagnosis and facilitate early intervention, we previously developed a newborn screening assay based on newly identified plasma bile acid biomarkers. Because the newborn screen had been validated using dried blood spots (DBS) from already diagnosed NPC1 patients, an unanswered question was whether the screen would be able to detect individuals with NPC1 at birth.

METHODS

To address this critical question, we obtained the newborn DBS for already diagnosed NPC1 subjects (n = 15) and carriers (n = 3) residing in California, New York, and Michigan states that archive residual DBS in biorepositories. For each of the DBS, we obtained two neighbor controls - DBS from patients born on the same day and in the same hospital as the NPC1 patients and carriers. 3β,5α,6β-trihydroxycholanic acid (bile acid A) and trihydroxycholanic acid glycine conjugate (bile acid B) were measured in the DBS using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay.

RESULTS

Bile acid B, the more specific biomarker for which the fully validated DBS assay was developed, was detected in 8/15 NPC1 patients, and elevated above the cut-off in 2/15 patients (the two samples with the shortest storage time). Bile acid B was detected in 2/2, 6/10, and 0/7 NPC1 samples that have been stored for <10.5 years, 13-20 years, and > 20 years, respectively, indicating that the glycine conjugate is detectable in DBS but may have reduced long-term stability compared with bile acid A, the precursor trihydroxycholanic acid, which was elevated in 15/15 NPC1 subjects, but not in carriers and controls.

CONCLUSIONS

These results demonstrate that newborn screening for NPC1 disease is feasible using bile acid biomarkers.

Recommendations for patient screening in ultra-rare inherited metabolic diseases: what have we learned from Niemann-Pick disease type C?

BACKGROUND

Rare and ultra-rare diseases (URDs) are often chronic and life-threatening conditions that have a profound impact on sufferers and their families, but many are notoriously difficult to detect. Niemann-Pick disease type C (NP-C) serves to illustrate the challenges, benefits and pitfalls associated with screening for ultra-rare inborn errors of metabolism (IEMs). A comprehensive, non-systematic review of published information from NP-C screening studies was conducted, focusing on diagnostic methods and study designs that have been employed to date. As a key part of this analysis, data from both successful studies (where cases were positively identified) and unsuccessful studies (where the chosen approach failed to identify any cases) were included alongside information from our own experiences gained from the planning and execution of screening for NP-C. On this basis, best-practice recommendations for ultra-rare IEM screening are provided. Twenty-six published screening studies were identified and categorised according to study design into four groups: 1) prospective patient cohort and family-based secondary screenings (18 studies); 2) analyses of archived 'biobank' materials (one study); 3) medical chart review and bioinformatics data mining (five studies); and 4) newborn screening (two studies). NPC1/NPC2 sequencing was the most common primary screening method (Sanger sequencing in eight studies and next-generation sequencing [gene panel or exome sequencing] in five studies), followed by biomarker analyses (usually oxysterols) and clinical surveillance.

CONCLUSIONS

Historically, screening for NP-C has been based on single-patient studies, small case series, and targeted cohorts, but the emergence of new diagnostic methods over the last 5-10 years has provided opportunities to screen for NP-C on a larger scale. Combining clinical, biomarker and genetic diagnostic methods represents the most effective way to identify NP-C cases, while reducing the likelihood of misdiagnosis. Our recommendations are intended as a guide for planning screening protocols for ultra-rare IEMs in general.

The impact of biomarkers analysis in the diagnosis of Niemann-Pick C disease and acid sphingomyelinase deficiency

BACKGROUND

Although representing two distinct disease entities, Niemann-Pick disease type C (NP-C) disease and acid sphingomyelinase deficiency (ASMD) share several phenotypic features. The lack of biomarkers was responsible in the past of diagnostic delay. Recently, plasma oxysterols, cholestan-3β,5α,6β-triol (Triol) and 7-ketocholesterol (7-KC) and lysosphingolipids, Lyso-sphingomyelin (Lyso-SM) and Lysosphingomyelin-509 (Lyso-SM-509), have been proposed as diagnostic biomarkers. We aimed to assess the diagnostic power of the two biomarkers categories and to evaluate possible correlations with patients' age and clinical phenotypes.

PATIENTS AND METHODS

We analyzed plasma oxysterols and lysosphingolipids in patients affected by NP-C and ASMD, and compared with healthy controls.

RESULTS

Oxysterols were always increased in both NP-C and ASMD. In NP-C, Lyso-SM and Lyso-SM-509 were increased in 70%, and 100% of patients, respectively. Biomarkers negatively correlated with patients' age, with highest levels in early-infantile, intermediate in the late-infantile and lowest in the juvenile phenotype. In ASMD, lysosphingolipids were both increased, with a greater order of magnitude than in NP-C, with highest levels in chronic-neurovisceral vs visceral phenotype.

CONCLUSIONS

Lysosphingolipids are useful biomarkers for a rapid and precise diagnosis, allowing clear distinction between NP-C and ASMD. They are more reliable biomarkers than oxysterols and correlate with patients' age and clinical phenotype.

Miglustat in Niemann-Pick disease type C patients: a review

OBJECTIVE

Niemann-Pick disease type C (NP-C) is a rare, autosomal recessive, neurodegenerative disease associated with a wide variety of progressive neurological manifestations. Miglustat is indicated for the treatment of progressive neurological manifestations in both adults and children. Since approval in 2009 there has been a vast growth in clinical experience with miglustat. The effectiveness of miglustat has been assessed using a range of measures.

METHODS

Comprehensive review of published data from studies of cellular neuropathological markers and structural neurological indices in the brain, clinical impairment/disability, specific clinical neurological manifestations, and patient survival.

RESULTS

Cranial diffusion tensor imaging and magnetic resonance spectroscopy studies have shown reduced levels of choline (a neurodegeneration marker), and choline/N-acetyl aspartate ratio (indicating increased neuronal viability) in the brain during up to 5 years of miglustat therapy, as well as a slowing of reductions in fractional anisotropy (an axonal/myelin integrity marker). A 2-year immunoassay study showed significant reductions in CSF-calbindin during treatment, indicating reduced cerebellar Purkinje cell loss. Magnetic resonance imaging studies have demonstrated a protective effect of miglustat on cerebellar and subcortical structure that correlated with clinical symptom severity. Numerous cohort studies assessing core neurological manifestations (impaired ambulation, manipulation, speech, swallowing, other) using NP-C disability scales indicate neurological stabilization over 2-8 years, with a trend for greater benefits in patients with older (non-infantile) age at neurological onset. A randomized controlled trial and several cohort studies have reported improvements or stabilization of saccadic eye movements during 1-5 years of therapy. Swallowing was also shown to improve/remain stable during the randomized trial (up to 2 years), as well as in long-term observational cohorts (up to 6 years). A meta-analysis of dysphagia - a potent risk factor for aspiration pneumonia and premature death in NP-C - demonstrated a survival benefit with miglustat due to improved/stabilized swallowing function.

CONCLUSIONS

The effects of miglustat on neurological NP-C manifestations has been assessed using a range of approaches, with benefits ranging from cellular changes in the brain through to visible clinical improvements and improved survival.

Contribution of tandem mass spectrometry to the diagnosis of lysosomal storage disorders

Tandem mass spectrometry (MS/MS) is a highly sensitive and specific technique. Thanks to the development of triple quadrupole analyzers, it is becoming more widely used in laboratories working in the field of inborn errors of metabolism. We review here the state of the art of this technique applied to the diagnosis of lysosomal storage disorders (LSDs) and how MS/MS has changed the diagnostic rationale in recent years. This fine technology brings more sensitive, specific, and reliable methods than the previous biochemical ones for the analysis of urinary glycosaminoglycans, oligosaccharides, and sialic acid. In sphingolipidoses, the quantification of urinary sphingolipids (globotriaosylceramide, sulfatides) is possible. The measurement of new plasmatic biomarkers such as oxysterols, bile acids, and lysosphingolipids allows the screening of many sphingolipidoses and related disorders (Niemann-Pick type C), replacing tedious biochemical techniques. Applied to amniotic fluid, a more reliable prenatal diagnosis or screening of LSDs is now available for fetuses presenting with antenatal manifestations. Applied to enzyme measurements, it allows high throughput assays for the screening of large populations, even newborn screening. The advent of this new method can modify the diagnostic rationale behind LSDs.

Consensus clinical management guidelines for Niemann-Pick disease type C

Niemann-Pick Type C (NPC) is a progressive and life limiting autosomal recessive disorder caused by mutations in either the NPC1 or NPC2 gene. Mutations in these genes are associated with abnormal endosomal-lysosomal trafficking, resulting in the accumulation of multiple tissue specific lipids in the lysosomes. The clinical spectrum of NPC disease ranges from a neonatal rapidly progressive fatal disorder to an adult-onset chronic neurodegenerative disease. The age of onset of the first (beyond 3 months of life) neurological symptom may predict the severity of the disease and determines life expectancy.

NPC has an estimated incidence of ~ 1: 100,000 and the rarity of the disease translate into misdiagnosis, delayed diagnosis and barriers to good care. For these reasons, we have developed clinical guidelines that define standard of care for NPC patients, foster shared care arrangements between expert centres and family physicians, and empower patients. The information contained in these guidelines was obtained through a systematic review of the literature and the experiences of the authors in their care of patients with NPC. We adopted the Appraisal of Guidelines for Research & Evaluation (AGREE II) system as method of choice for the guideline development process. We made a series of conclusive statements and scored them according to level of evidence, strengths of recommendations and expert opinions. These guidelines can inform care providers, care funders, patients and their carers of best practice of care for patients with NPC. In addition, these guidelines have identified gaps in the knowledge that must be filled by future research. It is anticipated that the implementation of these guidelines will lead to a step change in the quality of care for patients with NPC irrespective of their geographical location.

The Extending Spectrum of NPC1-Related Human Disorders: From Niemann-Pick C1 Disease to Obesity

The Niemann-Pick type C1 (NPC1) protein regulates the transport of cholesterol and fatty acids from late endosomes/lysosomes and has a central role in maintaining lipid homeostasis. NPC1 loss-of-function mutations in humans cause NPC1 disease, a rare autosomal-recessive lipid-storage disorder characterized by progressive and lethal neurodegeneration, as well as liver and lung failure, due to cholesterol infiltration. In humans, genome-wide association studies and post-genome-wide association studies highlight the implication of common variants in NPC1 in adult-onset obesity, body fat mass, and type 2 diabetes. Heterozygous human carriers of rare loss-of-function coding variants in NPC1 display an increased risk of morbid adult obesity. These associations have been confirmed in mice models, showing an important interaction with high-fat diet. In this review, we describe the current state of knowledge for NPC1 variants in relationship to pleiotropic effects on metabolism. We provide evidence that NPC1 gene variations may predispose to common metabolic diseases by modulating steroid hormone synthesis and/or lipid homeostasis. We also propose several important directions of research to further define the complex roles of NPC1 in metabolism. This review emphasizes the contribution of NPC1 to obesity and its metabolic complications.

Elevation of plasma lysosphingomyelin-509 and urinary bile acid metabolite in Niemann-Pick disease type C-affected individuals

Niemann-Pick disease type C (NPC) is a neurovisceral disorder associated with the accumulation of lipids such as cholesterol and sphingolipids. NPC is caused by either NPC1 or NPC2, which encode lysosomal proteins located at membraneous and soluble fractions, respectively. For the past decade, the oxidation products of cholesterol, such as cholestane-3β,5α,6β-triol and 7-ketocholesterol, have been considered selective biomarkers for NPC. However, recent evidence has indicated numerous novel biomarkers for NPC, which raises the possibility that the diagnosis of NPC might be associated with the elevation of multiple lipid biomarkers, rather than a single biomarker. Sphingosylphosphorylcholine (SPC) has been suggested to be one such biomarker for NPC, in which elevated sphingomyelin is a potential precursor. Thus, we first performed a validation study of plasma SPC using LC-MS/MS. The results showed the following plasma concentrations in the NPC-affected and control individuals, respectively: 8.2 ± 2.8 nM (mean ± SD; median, 7.0 nM; max, 11.7 nM; min, 5.1 nM; n = 5) and 3.1 ± 1.4 nM (median, 2.9 nM; max, 4.8 nM; min, 1.5 nM; n = 7). We further extended the study to plasma lysophingomyelin-509 for NPC, a newly reported biomarker with uncharacterized chemical nature. Based on these result with plasma SPC as a surrogate marker, the value of mean of median of plasma lysophingomyelin-509 in NPC-affected individuals elevated at 65.2 (max, 73.2; min, 26.7; n = 5). Furthermore, the efficacy of plasma SPC and lysosphingomyelin-509 as promising biomarkers for this disorder was supported by the finding that the urinary concentration of 3β-sulfooxy-7β-N-acetylglucosaminyl-5-cholen-24-oic acid, an established biomarker for NPC, was also elevated in the NPC-affected individuals. These results suggest that a novel combination of plasma biomarkers, such as SPC and/or lysophingomyelin-509, and urinary bile acid metabolite could offer a promising platform for the diagnosis of NPC.

Rapid screening for lipid storage disorders using biochemical markers. Expert center data and review of the literature

BACKGROUND

In patients suspected of a lipid storage disorder (sphingolipidoses, lipidoses), confirmation of the diagnosis relies predominantly on the measurement of specific enzymatic activities and genetic studies. New UPLC-MS/MS methods have been developed to measure lysosphingolipids and oxysterols, which, combined with chitotriosidase activity may represent a rapid first tier screening for lipid storage disorders.

MATERIAL AND METHODS

A lysosphingolipid panel consisting of lysoglobotriaosylceramide (LysoGb3), lysohexosylceramide (LysoHexCer: both lysoglucosylceramide and lysogalactosylceramide), lysosphingomyelin (LysoSM) and its carboxylated analogue lysosphingomyelin-509 (LysoSM-509) was measured in control subjects and plasma samples of predominantly untreated patients affected with lipid storage disorders (n=74). In addition, the oxysterols cholestane-3β,5α,6β-triol and 7-ketocholesterol were measured in a subset of these patients (n=36) as well as chitotriosidase activity (n=43). A systematic review of the literature was performed to assess the usefulness of these biochemical markers.

RESULTS

Specific elevations of metabolites, i.e. without overlap between controls and other lipid storage disorders, were found for several lysosomal storage diseases: increased LysoSM levels in acid sphingomyelinase deficiency (Niemann-Pick disease type A/B), LysoGb3 levels in males with classical phenotype Fabry disease and LysoHexCer (i.e. lysoglucosylceramide/lysogalactosylceramide) in Gaucher and Krabbe diseases. While elevated levels of LysoSM-509 and cholestane-3β,5α,6β-triol did not discriminate between Niemann Pick disease type C and acid sphingomyelinase deficiency, LysoSM-509/LysoSM ratio was specifically elevated in Niemann-Pick disease type C. In Gaucher disease type I, mild increases in several lysosphingolipids were found including LysoGb3 with levels in the range of non-classical Fabry males and females. Chitotriosidase showed specific elevations in symptomatic Gaucher disease, and was mildly elevated in all other lipid storage disorders. Review of the literature identified 44 publications. Most findings were in line with our cohort. Several moderate elevations of biochemical markers were found across a wide range of other, mainly inherited metabolic, diseases.

CONCLUSION

Measurement in plasma of LysoSLs and oxysterols by UPLC-MS/MS in combination with activity of chitotriosidase provides a useful first tier screening of patients suspected of lipid storage disease. The LysoSM-509/LysoSM ratio is a promising parameter in Niemann-Pick disease type C. Further studies in larger groups of untreated patients and controls are needed to improve the specificity of the findings.

Lipid biomarkers for the peroxisomal and lysosomal disorders: their formation, metabolism and measurement

Lipid biomarkers play important roles in the diagnosis of and monitoring of treatment in peroxisomal disorders and lysosomal storage disorders. Today, a variety of lipids, including very long chain fatty acids, glycolipids, bile acids and the oxidation products of cholesterol, have been considered as biomarkers for these disorders. In this brief review, the authors summarized the recent advances regarding these lipid biomarkers in terms of their formation, metabolism and measurement in these disorders. An understanding of these biomarkers will offer a key to the development of novel diagnoses and help create more effective therapies in the future.

Laboratory investigations

This chapter deals with chemical and hematologic investigations which are often considered in the diagnostic workup of subacute to chronic cerebellar ataxias. Relevant investigations in blood (serum, plasma), urine, and cerebrospinal fluid are discussed. Particular attention is paid to early diagnosis of treatable metabolic ataxias (such as abetalipoproteinemia, coenzyme Q10 deficiency, cerebrotendinous xanthomatosis, glucose transporter type 1 deficiency, Refsum disease, and vitamin E deficiency), but autoimmune ataxias, other vitamin deficiencies, and endocrine disorders should also be kept in mind. Adequate interpretation of test results has to consider age-specific reference values. The selection of investigations should mainly be driven by the overall clinical context, considering gender, history, age, and mode of presentation, cerebellar and other neurologic as well as extraneurologic findings.

Recommendations for the detection and diagnosis of Niemann-Pick disease type C: An update

Purpose of review:

Niemann-Pick disease type C (NP-C) is a neurovisceral disorder that may be more prevalent than earlier estimates. Diagnosis of NP-C is often delayed; a key aim for clinical practice is to reduce this delay. Recently, substantial progress has been made in the field of NP-C screening and diagnosis, justifying an update to the existing recommendations for clinical practice.

Recent findings:

New biomarker profiling and genetic analysis technologies are included as first-line diagnostic tests for NP-C. Most diagnoses can now be confirmed by combination of biomarker and genetic analyses. Filipin staining may facilitate diagnosis in uncertain cases. Recommendations are provided for psychiatrists, neuro-ophthalmologists, and radiologists, and on screening within specific at-risk patient cohorts. The NP-C diagnostic algorithm has been updated and simplified.

Summary:

This publication provides expert recommendations for clinicians who may see patients presenting with the signs and symptoms of NP-C, including general practitioners, pediatricians, neurologists, and psychiatrists.

Non-immune fetal hydrops of metabolic origin: a case report and a review of the literature

Aim

To propose a diagnostic algorithm for non-immune fetal hydrops (NIFH) of metabolic origin based on a review of the literature and on the workup of a clinical case.

Background

The etiology of NIFH is complex and remains unexplained in 15%–25% of patients. The appropriate work up beyond an initial approach is still not well defined but it should include screening for metabolic conditions. Inborn errors of metabolism comprise a heterogeneous group of autosomal recessive rare inherited disorders, among which lysosomal storage disorder is the most common subtype.

Case description

We report a case of a 30-year-old pregnant, primiparous woman, referred to a tertiary hospital at 22 weeks of gestation because of a fetal hydrops. The second trimester obstetric ultrasound showed a hydrothorax and a large subcutaneous edema. At 30 weeks of gestation, the fetal health status deteriorated and a massive hepatomegaly was detected. The metabolic study of the amniotic fluid supernatant suggested a lysosomal disease. The ominous prognosis of the condition motivated the parents to opt for a termination of pregnancy. The autopsy study confirmed the existence of a metabolic disease.

Conclusion

The incidence of inborn errors of metabolism may be significantly higher in NIHF than reported previously. Consequently, an extensive investigation for the etiology of NIHF including the screening for metabolic disorders seems to be crucial for a definitive diagnosis.

Clinical relevance

Despite the lack of treatment options for the majority of these disorders, it is of great importance to follow an established workup, in order to identify the index case as soon as possible, as pregnancy management decisions and prenatal counselling in future pregnancies will depend on a more precise diagnosis.

Activation of PKC triggers rescue of NPC1 patient specific iPSC derived glial cells from gliosis

BACKGROUND

Niemann-Pick disease Type C1 (NPC1) is a rare progressive neurodegenerative disorder caused by mutations in the NPC1 gene. The pathological mechanisms, underlying NPC1 are not yet completely understood. Especially the contribution of glial cells and gliosis to the progression of NPC1, are controversially discussed. As an analysis of affected cells is unfeasible in NPC1-patients, we recently developed an in vitro model system, based on cells derived from NPC1-patient specific iPSCs. Here, we asked if this model system recapitulates gliosis, observed in non-human model systems and NPC1 patient post mortem biopsies. We determined the amount of reactive astrocytes and the regulation of the intermediate filaments GFAP and vimentin, all indicating gliosis. Furthermore, we were interested in the assembly and phosphorylation of these intermediate filaments and finally the impact of the activation of protein kinase C (PKC), which is described to ameliorate the pathogenic phenotype of NPC1-deficient fibroblasts, including hypo-phosphorylation of vimentin and cholesterol accumulation.

METHODS

We analysed glial cells derived from NPC1 patient specific induced pluripotent stem cells, carrying different NPC1 mutations. The amount of reactive astrocytes was determined by means of immuncytochemical stainings and FACS-analysis. Semi-quantitative western blot was used to determine the amount of phosphorylated GFAP and vimentin. Cholesterol accumulation was analysed by Filipin staining and quantified by Amplex Red Assay. U18666A was used to induce NPC1 phenotype in unaffected cells of the control cell line. Phorbol 12-myristate 13-acetate (PMA) was used to activate PKC.

RESULTS

Immunocytochemical detection of GFAP, vimentin and Ki67 revealed that NPC1 mutant glial cells undergo gliosis. We found hypo-phosphorylation of the intermediate filaments GFAP and vimentin and alterations in the assembly of these intermediate filaments in NPC1 mutant cells. The application of U18666A induced not only NPC1 phenotypical accumulation of cholesterol, but characteristics of gliosis in glial cells derived from unaffected control cells. The application of phorbol 12-myristate 13-acetate, an activator of protein kinase C resulted in a significantly reduced number of reactive astrocytes and further characteristics of gliosis in NPC1-deficient cells. Furthermore, it triggered a restoration of cholesterol amounts to level of control cells.

CONCLUSION

Our data demonstrate that glial cells derived from NPC1-patient specific iPSCs undergo gliosis. The application of U18666A induced comparable characteristics in un-affected control cells, suggesting that gliosis is triggered by hampered function of NPC1 protein. The activation of protein kinase C induced an amelioration of gliosis, as well as a reduction of cholesterol amount. These results provide further support for the line of evidence that gliosis might not be only a secondary reaction to the loss of neurons, but might be a direct consequence of a reduced PKC activity due to the phenotypical cholesterol accumulation observed in NPC1. In addition, our data support the involvement of PKCs in NPC1 disease pathogenesis and suggest that PKCs may be targeted in future efforts to develop therapeutics for NPC1 disease.

LC-MS/MS multiplex analysis of lysosphingolipids in plasma and amniotic fluid: A novel tool for the screening of sphingolipidoses and Niemann-Pick type C disease

Background

The biological diagnosis of sphingolipidoses currently relies on the measurement of specific enzymatic activities and/or genetic studies. Lysosphingolipids have recently emerged as potential biomarkers of sphingolipidoses and Niemann-Pick type C in plasma.

Methodology

We developed a sensitive and specific method enabling the simultaneous quantification of lysosphingolipids by LC-MS/MS: lysoglobotriaosylceramide for Fabry disease, lysohexosylceramide (i.e. lysoglucosylceramide and/or lysogalactosylceramide) for Gaucher and Krabbe diseases, lysosphingomyelin and its carboxylated analogue lysosphingomyelin-509 for Niemann-Pick type A or B, and C diseases, lysoGM1 ganglioside for GM1gangliosidosis and lysoGM2 ganglioside for GM2 gangliosidosis.

Findings

The diagnostic performances were validated in plasma samples analysing a large series of patients affected with sphingolipidoses and Niemann-Pick type C disease (n = 98), other inborn errors of metabolism (n = 23), and controls (n = 228). The multiplex measurement of lysosphingolipids allowed the screening of Fabry (including female patients and late-onset variants), Gaucher and infantile Krabbe, Niemann-Pick type A/B and C diseases with high sensitivity and specificity. LysoGM1 and LysoGM2 were elevated in most of the patients affected with GM1 and GM2 gangliosidosis respectively.

In amniotic fluid supernatant from pregnancies presenting non-immune hydrops fetalis (n = 77, including previously diagnosed Gaucher (n = 5), GM1 gangliosidosis (n = 4) and galactosialidosis (n = 4) fetuses) and from normal pregnancies (n = 15), a specific and dramatic increase of lysohexosylceramide was observed only in the Gaucher amniotic fluid samples.

Interpretation

This multiplex assay which allows the simultaneous measurement of lysosphingolipids in plasma modifies the diagnostic strategy of sphingolipidoses and Niemann-Pick type C. Furthermore, in pregnancies presenting non-immune hydrops fetalis, lysohexosylceramide measurement in amniotic fluid offers a rapid screening of fetal Gaucher disease without waiting for glucocerebrosidase activity measurement in cultured amniocytes.

NMR analysis reveals significant differences in the plasma metabolic profiles of Niemann Pick C1 patients, heterozygous carriers, and healthy controls

Niemann-Pick type C1 (NPC1) disease is a rare autosomal recessive, neurodegenerative lysosomal storage disorder, which presents with a range of clinical phenotypes and hence diagnosis remains a challenge. In view of these difficulties, the search for a novel, NPC1-specific biomarker (or set of biomarkers) is a topic of much interest. Here we employed high-resolution ¹H nuclear magnetic resonance spectroscopy coupled with advanced multivariate analysis techniques in order to explore and seek differences between blood plasma samples acquired from NPC1 (untreated and miglustat treated), heterozygote, and healthy control subjects. Using this approach, we were able to identify NPC1 disease with 91% accuracy confirming that there are significant differences in the NMR plasma metabolic profiles of NPC1 patients when compared to healthy controls. The discrimination between NPC1 (both miglustat treated and untreated) and healthy controls was dominated by lipoprotein triacylglycerol ¹H NMR resonances and isoleucine. Heterozygote plasma samples displayed also increases in the intensities of selected lipoprotein triacylglycerol ¹H NMR signals over those of healthy controls. The metabolites identified could represent useful biomarkers in the future and provide valuable insight in to the underlying pathology of NPC1 disease.

Childhood leukodystrophies: A literature review of updates on new definitions, classification, diagnostic approach and management

Childhood leukodystrophies are a growing category of neurological disorders in pediatric neurology practice. With the help of new advanced genetic studies such as whole exome sequencing (WES) and whole genome sequencing (WGS), the list of childhood heritable white matter disorders has been increased to more than one hundred disorders. During the last three decades, the basic concepts and definitions, classification, diagnostic approach and medical management of these disorders much have changed. Pattern recognition based on brain magnetic resonance imaging (MRI), has played an important role in this process. We reviewed the last Global Leukodystrophy Initiative (GLIA) expert opinions in definition, new classification, diagnostic approach and medical management including emerging treatments for pediatric leukodystrophies.

The hidden Niemann-Pick type C patient: clinical niches for a rare inherited metabolic disease

BACKGROUND

Niemann-Pick disease type C (NP-C) is a rare, inherited neurodegenerative disease of impaired intracellular lipid trafficking. Clinical symptoms are highly heterogeneous, including neurological, visceral, or psychiatric manifestations. The incidence of NP-C is under-estimated due to under-recognition or misdiagnosis across a wide range of medical fields. New screening and diagnostic methods provide an opportunity to improve detection of unrecognized cases in clinical sub-populations associated with a higher risk of NP-C. Patients in these at-risk groups ("clinical niches") have symptoms that are potentially related to NP-C, but go unrecognized due to other, more prevalent clinical features, and lack of awareness regarding underlying metabolic causes.

METHODS

Twelve potential clinical niches identified by clinical experts were evaluated based on a comprehensive, non-systematic review of literature published to date. Relevant publications were identified by targeted literature searches of EMBASE and PubMed using key search terms specific to each niche. Articles published in English or other European languages up to 2016 were included.

FINDINGS

Several niches were found to be relevant based on available data: movement disorders (early-onset ataxia and dystonia), organic psychosis, early-onset cholestasis/(hepato)splenomegaly, cases with relevant antenatal findings or fetal abnormalities, and patients affected by family history, consanguinity, and endogamy. Potentially relevant niches requiring further supportive data included: early-onset cognitive decline, frontotemporal dementia, parkinsonism, and chronic inflammatory CNS disease. There was relatively weak evidence to suggest amyotrophic lateral sclerosis or progressive supranuclear gaze palsy as potential niches.

CONCLUSIONS

Several clinical niches have been identified that harbor patients at increased risk of NP-C.

Quantitation of plasmatic lysosphingomyelin and lysosphingomyelin-509 for differential screening of Niemann-Pick A/B and C diseases

Acid sphingomyelinase deficiency (ASMd, Niemann-Pick disease A/B) and Niemann-Pick type C disease (NPC) share core clinical symptoms. Initial diagnostic discrimination of these two rare lysosomal storage diseases is thus difficult. As sphingomyelin accumulates in ASMd as well as NPC, lysosphingomyelin (sphingosylphosphorylcholine) and its m/z 509 analog were suggested as biomarkers for both diseases. Herein we present results of simultaneous LC-ESI-MS/MS measurements of lysosphingomyelin and lysosphingomyelin 509 in plasma and dried blood spots (DBS) collected from ASMd and NPC patients and suggest that the plasma but not DBS levels of the two analytes allow differential biochemical screening of ASMd and NPC.

Differences in Niemann-Pick disease Type C symptomatology observed in patients of different ages

BACKGROUND

Niemann-Pick disease Type C (NP-C) is a genetic lipid storage disorder characterised by progressive neurovisceral symptomatology. Typically, disease progression is more pronounced in patients with early onset of neurological symptoms. Heterogeneous clinical presentation may hinder disease recognition and lead to delays in diagnosis. Here we describe the prevalence of signs and symptoms observed in patients with NP-C and analyse the relationship between these symptoms in different age groups.

METHODS

The combined patient cohort used in the analyses comprised NP-C cases (n=164) and controls (n=135) aged 0 to 60years from two previously published cohorts; a cohort of all ages from which patients ≤4years of age were excluded and a cohort with early-onset NP-C and age-matched controls. The analysis of relationships between different signs and symptoms was performed for both NP-C cases and controls in two sub-groups, ≤4 and >4years of age, using cluster analyses. The threshold of 4years of age was selected to reflect the minimum age cut-off for satisfactory discriminatory power of the original NP-C SI. To assess the prevalence of individual signs and symptoms at age of diagnosis, patients were categorised by age into 5-year sub-groups, and prevalence values estimated for each sign and symptom of NP-C.

RESULTS

Two main clusters of symptoms were clearly defined for NP-C cases in each age sub-group, whereas clusters were not as clearly defined for controls. For NP-C cases ≤4years of age, one cluster comprised exclusively visceral symptoms; the second cluster combined all other signs and symptoms in this age group. For NP-C cases >4years of age, each cluster contained a mixture of visceral, neurological and psychiatric items. Prevalence estimations showed that visceral symptoms (e.g. isolated unexplained splenomegaly) were most common in NP-C cases ≤4years of age. Neurological symptoms were generally more common in NP-C cases >4years of age than in younger patients, with the exception of hypotonia and delayed developmental milestones.

CONCLUSIONS

These analyses provide a comprehensive overview of symptomatology observed in a large combined cohort of patients with NP-C and controls across a wide range of ages. The results largely reflect observations from clinical practice and support the importance of multi-disciplinary approaches for identification of patients with NP-C, taking into account age-specific manifestations and their possible correlations.

Disorders in the initial steps of steroid hormone synthesis

Steroidogenesis begins with cellular internalization of low-density lipoprotein particles and subsequent intracellular processing of cholesterol. Disorders in these steps include Adrenoleukodystrophy, Wolman Disease and its milder variant Cholesterol Ester Storage Disease, and Niemann-Pick Type C Disease, all of which may present with adrenal insufficiency. The means by which cholesterol is directed to steroidogenic mitochondria remains incompletely understood. Once cholesterol reaches the outer mitochondrial membrane, its delivery to the inner mitochondrial membrane is regulated by the steroidogenic acute regulatory protein (StAR). Severe StAR mutations cause classic congenital lipoid adrenal hyperplasia, characterized by lipid accumulation in the adrenal, adrenal insufficiency, and disordered sexual development in 46,XY individuals. The lipoid CAH phenotype, including spontaneous puberty in 46,XX females, is explained by a two-hit model. StAR mutations that retain partial function cause a milder, non-classic disease characterized by glucocorticoid deficiency, with lesser disorders of mineralocorticoid and sex steroid synthesis. Once inside the mitochondria, cholesterol is converted to pregnenolone by the cholesterol side-chain cleavage enzyme, P450scc, encoded by the CYP11A1 gene. Rare patients with mutations of P450scc are clinically and hormonally indistinguishable from those with lipoid CAH, and may also present as milder non-classic disease. Patients with P450scc defects do not have the massive adrenal hyperplasia that characterizes lipoid CAH, but adrenal imaging may occasionally fail to distinguish these, necessitating DNA sequencing.

Diagnosis of sphingolipidoses: a new simultaneous measurement of lysosphingolipids by LC-MS/MS

Background:

Lysosphingolipids (LysoSLs) are derivatives of sphingolipids which have lost the amide-linked acyl chain. More recently, LysoSLs have been identified as storage compounds in several sphingolipidoses, including Gaucher, Fabry and Niemann-Pick diseases. To date, different methods have been developed to measure each individual lysosphingolipid in plasma. This report describes a rapid liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) assay for simultaneous quantification of several LysoSLs in plasma.

Methods:

We analyzed the following compounds: hexosylsphingosine (HexSph), globotriaosylsphingosine (LysoGb3), lysosphingomyelin (LysoSM) and lysosphingomyelin-509 (LysoSM-509). The sample preparation requires only 100 μL of plasma and consists of an extraction with a mixture of MeOH/acetone/H

Results:

The method validation showed high sensitivity, an excellent accuracy and precision. Reference ranges were determined in healthy adult and pediatric population. The results demonstrate that the LC-MS/MS method can quantify different LysoSLs and can be used to identify patients with Fabry (LysoGb3), Gaucher and Krabbe (HexSph) diseases, prosaposine deficiency (LysoGb3 and HexSph), and Niemann-Pick disease types A/B and C (LysoSM and LysoSM-509).

Conclusions:

This LC-MS/MS method allows a rapid and simultaneous quantification of LysoSLs and is useful as a biochemical diagnostic tool for sphingolipidoses.

Biomarkers in Lysosomal Storage Diseases

A biomarker is generally an analyte that indicates the presence and/or extent of a biological process, which is in itself usually directly linked to the clinical manifestations and outcome of a particular disease. The biomarkers in the field of lysosomal storage diseases (LSDs) have particular relevance where spectacular therapeutic initiatives have been achieved, most notably with the introduction of enzyme replacement therapy (ERT). There are two main types of biomarkers. The first group is comprised of those molecules whose accumulation is directly enhanced as a result of defective lysosomal function. These molecules represent the storage of the principal macro-molecular substrate(s) of a specific enzyme or protein, whose function is deficient in the given disease. In the second group of biomarkers, the relationship between the lysosomal defect and the biomarker is indirect. In this group, the biomarker reflects the effects of the primary lysosomal defect on cell, tissue, or organ functions. There is no “gold standard” among biomarkers used to diagnosis and/or monitor LSDs, but there are a number that exist that can be used to reasonably assess and monitor the state of certain organs or functions. A number of biomarkers have been proposed for the analysis of the most important LSDs. In this review, we will summarize the most promising biomarkers in major LSDs and discuss why these are the most promising candidates for screening systems.

Diversity of glycosphingolipid GM2 and cholesterol accumulation in NPC1 patient-specific iPSC-derived neurons

Niemann-Pick disease Type C1 (NPC1) is a rare progressive neurodegenerative disorder caused by mutations in the NPC1 gene. On the cellular level NPC1 mutations lead to an accumulation of cholesterol and gangliosides. As a thorough analysis of the severely affected neuronal cells is unfeasible in NPC1 patients, we recently described the cellular phenotype of neuronal cells derived from NPC1 patient iPSCs carrying the compound heterozygous mutation c.1836A>C/c.1628delC. Here we expanded the analysis to cell lines carrying the prevalent mutation c.3182T>C and the novel mutation c.1180T>C, as well as to the determination of GM2 and GM3 gangliosides in NPC1 patient-specific iPSC-derived neurons and glia cells. Immunocytochemical detection of GM2 revealed punctated staining pattern predominantly localized in neurons. Detection of cholesterol by filipin staining showed a comparable staining pattern, colocalized with GM2, indicating a deposit of GM2 and cholesterol in the same cellular compartments. Accumulations were not only restricted to cell bodies, but were also found in the neuronal extensions. A quantification of the GM2 amount by HPLC-MS/MS confirmed significantly higher amounts in neurons carrying a mutation. Additionally, these cells displayed a lowered activity of the catabolic enzyme Hex A, but not B4GALNT1. Molecular docking simulations indicated binding of cholesterol to Hex A, suggesting cholesterol influences the GM2 degradation pathway and, subsequently, leading to the accumulation of GM2. Taken together, this is the first study showing an accumulation of GM2 in neuronal derivatives of patient-specific iPSCs and thus proving further disease-specific hallmarks in this human in vitro model of NPC1.

Tandem Mass Spectrometry of Sphingolipids: Applications for Diagnosis of Sphingolipidoses

In recent years, mass spectrometry (MS) has become the dominant technology in lipidomic analysis. It is widely used in diagnosis and research of lipid metabolism disorders including those characterized by impairment of lysosomal functions and storage of nondegraded-degraded substrates. These rare diseases, which include sphingolipidoses, have severe and often fatal clinical consequences. Modern MS methods have contributed significantly to achieve a definitive diagnosis, which is essential in clinical practice to begin properly targeted patient care. Here we summarize MS and tandem MS methods used for qualitative and quantitative analysis of sphingolipids (SL) relative to the diagnostic process for sphingolipidoses and studies focusing on alterations in cell functions due to these disorders. This review covers the following topics: Tandem MS is sensitive and robust in determining the composition of sphingolipid classes in various biological materials. Its ability to establish SL metabolomic profiles using MS bench-top analyzers, significantly benefits the first stages of a diagnosis as well as metabolic studies of these disorders. It can thus contribute to a better understanding of the biological significance of SL.

Antenatal manifestations of inborn errors of metabolism: biological diagnosis

Inborn errors of metabolism (IEMs) that present with abnormal imaging findings in the second half of pregnancy are mainly lysosomal storage disorders (LSDs), cholesterol synthesis disorders (CSDs), glycogen storage disorder type IV (GSD IV), peroxisomal disorders, mitochondrial fatty acid oxidation defects (FAODs), organic acidurias, aminoacidopathies, congenital disorders of glycosylation (CDGs), and transaldolase deficiency. Their biological investigation requires fetal material. The supernatant of amniotic fluid (AF) is useful for the analysis of mucopolysaccharides, oligosaccharides, sialic acid, lysosphingolipids and some enzyme activities for LSDs, 7- and 8-dehydrocholesterol, desmosterol and lathosterol for CSDs, acylcarnitines for FAODs, organic acids for organic acidurias, and polyols for transaldolase deficiency. Cultured AF or fetal cells allow the measurement of enzyme activities for most IEMs, whole-cell assays, or metabolite measurements. The cultured cells or tissue samples taken after fetal death can be used for metabolic profiling, enzyme activities, and DNA extraction. Fetal blood can also be helpful. The identification of vacuolated cells orients toward an LSD, and plasma is useful for diagnosing peroxisomal disorders, FAODs, CSDs, some LSDs, and possibly CDGs and aminoacidopathies. We investigated AF of 1700 pregnancies after exclusion of frequent etiologies of nonimmune hydrops fetalis and identified 108 fetuses affected with LSDs (6.3 %), 29 of them with mucopolysaccharidosis type VII (MPS VII), and six with GSD IV (0.3 %). In the AF of 873 pregnancies, investigated because of intrauterine growth restriction and/or abnormal genitalia, we diagnosed 32 fetuses affected with Smith-Lemli-Opitz syndrome (3.7 %).

1H NMR-Linked Metabolomics Analysis of Liver from a Mouse Model of NP-C1 Disease

Clinical manifestations of Niemann-Pick type C1 (NP-C1) disease include neonatal hepatosplenomegaly and in some patients progressive liver dysfunction and failure. This study involved a ¹H NMR-linked metabolomics analysis of liver samples collected from a NP-C1 disease mutant mouse model in order to explore time-dependent imbalances in metabolic pathways associated with NP-C1 liver dysfunction, including fibrosis. NP-C1 mutant (Npc1^-/-; NP-C1), control (Npc1^+/+; WT), and NP-C1 heterozygous mice (Npc1^+/-; HET) were generated from heterozygote matings. Aqueous extracts of these liver samples collected at time points of 3, 6, 9, and 11 weeks were subjected to high-resolution NMR analysis, and multivariate (MV) metabolomics analyses of data sets acquired were performed. A MV random forests (RFs) model effectively discriminated between NP-C1 and a combined WT/HET hepatic NMR profiles with very high predictive accuracy and reliability. Key distinguishing features included significant upregulations in the hepatic concentrations of phenylalanine, tyrosine, glutamate, lysine/ornithine, valine, threonine, and hypotaurine/methionine, and diminished levels of nicotinate/niacinamide, inosine, phosphoenolpyruvate, and 3-hydroxyphenylacetate. Quantitative pathway topological analysis confirmed that imbalances in tyrosine biosynthesis, and hepatic phenylalanine, tyrosine, glutamate/glutamine, and nicotinate/niacinamide metabolism were involved in the pathogenesis of NP-C1 disease-associated liver dysfunction/damage. ¹H NMR-linked metabolomics analysis provides valuable biomarker information regarding hepatic dysfunction or damage in NP-C1 disease.

Cerebrospinal Fluid Calbindin D Concentration as a Biomarker of Cerebellar Disease Progression in Niemann-Pick Type C1 Disease

Niemann-Pick type C (NPC) 1 disease is a rare, inherited, neurodegenerative disease. Clear evidence of the therapeutic efficacy of 2-hydroxypropyl-β-cyclodextrin (HPβCD) in animal models resulted in the initiation of a phase I/IIa clinical trial in 2013 and a phase IIb/III trial in 2015. With clinical trials ongoing, validation of a biomarker to track disease progression and serve as a supporting outcome measure of therapeutic efficacy has become compulsory. In this study, we evaluated calcium-binding protein calbindin D-28K (calbindin) concentrations in the cerebrospinal fluid (CSF) as a biomarker of NPC1 disease. In the naturally occurring feline model, CSF calbindin was significantly elevated at 3 weeks of age, prior to the onset of cerebellar dysfunction, and steadily increased to >10-fold over normal at end-stage disease. Biweekly intrathecal administration of HPβCD initiated prior to the onset of neurologic dysfunction completely normalized CSF calbindin in NPC1 cats at all time points analyzed when followed up to 78 weeks of age. Initiation of HPβCD after the onset of clinical signs (16 weeks of age) resulted in a delayed reduction of calbindin levels in the CSF. Evaluation of CSF from patients with NPC1 revealed that calbindin concentrations were significantly elevated compared with CSF samples collected from unaffected patients. Off-label treatment of patients with NPC1 with miglustat, an inhibitor of glycosphingolipid biosynthesis, significantly decreased CSF calbindin compared with pretreatment concentrations. These data suggest that the CSF calbindin concentration is a sensitive biomarker of NPC1 disease that could be instrumental as an outcome measure of therapeutic efficacy in ongoing clinical trials.

Diagnostic tests for Niemann-Pick disease type C (NP-C): A critical review

Niemann-Pick disease type C (NP-C) is a neurovisceral lysosomal cholesterol trafficking and lipid storage disorder caused by mutations in one of the two genes, NPC1 or NPC2. Diagnosis has often been a difficult task, due to the wide range in age of onset of NP-C and clinical presentation of the disease, combined with the complexity of the cell biology (filipin) laboratory testing, even in combination with genetic testing. This has led to substantial delays in diagnosis, largely depending on the access to specialist centres and the level of knowledge about NP-C of the physician in the area. In recent years, advances in mass spectrometry has allowed identification of several sensitive plasma biomarkers elevated in NP-C (e.g. cholestane-3β,5α,6β-triol, lysosphingomyelin isoforms and bile acid metabolites), which, together with the concomitant progress in molecular genetic technology, have greatly impacted the strategy of laboratory testing. Specificity of the biomarkers is currently under investigation and other pathologies are being found to also result in elevations. Molecular genetic testing also has its limitations, notably with unidentified mutations and the classification of new variants. This review is intended to increase awareness on the currently available approaches to laboratory diagnosis of NP-C, to provide an up to date, comprehensive and critical evaluation of the various techniques (cell biology, biochemical biomarkers and molecular genetics), and to briefly discuss ongoing/future developments. The use of current tests in proper combination enables a rapid and correct diagnosis in a large majority of cases. However, even with recent progress, definitive diagnosis remains challenging in some patients, for whom combined genetic/biochemical/cytochemical markers do not provide a clear answer. Expertise and reference laboratories thus remain essential, and further work is still required to fulfill unmet needs.

Diagnostic workup and management of patients with suspected Niemann-Pick type C disease

Niemann-Pick type C (NP-C) disease is a neurovisceral disorder caused by mutations in the NPC1 and NPC2 genes. It is characterized by lysosomal storage of a broad range of lipids as a result of abnormal intracellular lipid trafficking. Typically patients develop neurodegeneration; however, the speed of disease progression is variable. The exact functions of NPC1 and NPC2 proteins have not been determined and therefore the molecular pathophysiology of NP-C is still not clearly understood. Due to the disease's rarity and clinical heterogeneity, delays from symptom onset to diagnosis and treatment initiation are common. Current therapeutic approaches focus on multidisciplinary symptom control and deceleration (rather than reversal) of disease progression. Thus identification of cases at early stages of disease is particularly important. Recent advances in genetic and biochemical testing have resulted in the generation of relatively non-invasive, quick and cost-effective laboratory assays that are highly sensitive and specific and have the capacity to enhance the clinicians' ability to reach a diagnosis earlier. Miglustat is a compound recently licensed in many countries for the treatment of NP-C that has been shown to decelerate neurological regression, whereas many other promising drugs are currently being trialled in preclinical models or human studies. This review summarizes key clinical, genetic and biochemical features of NP-C, suggests a simple diagnostic investigation strategy and gives an overview of available therapeutic options as well as potential novel treatments currently under development.

Lyso-glycosphingolipid abnormalities in different murine models of lysosomal storage disorders

In lysosomal glycosphingolipid storage disorders, marked elevations in corresponding glycosphingoid bases (lyso-glycosphingolipids) have been reported, such as galactosylsphingosine in Krabbe disease, glucosylsphingosine in Gaucher disease and globotriaosylsphingosine in Fabry disease. Using LC–MS/MS, we comparatively investigated the occurrence of abnormal lyso-glycosphingolipids in tissues and plasma of mice with deficiencies in lysosomal α-galactosidase A, glucocerebrosidase and galactocerebrosidase. The nature and specificity of lyso-glycosphingolipid abnormalities are reported and compared to that in correspondingly more abundant N-acylated glycosphingolipids. Specific elevations in tissue and plasma globotriaosylsphingosine were detected in α-galactosidase A-deficient mice; glucosylsphingosine in glucocerebrosidase-deficient mice and galactosylsphingosine in galactocerebrosidase-deficient animals. A similar investigation was conducted for two mouse models of Niemann Pick type C (Npc1nih and Npc1nmf164), revealing significant tissue elevation of several neutral glycosphingolipids and concomitant increased plasma glucosylsphingosine. This latter finding was recapitulated by analysis of plasma of NPC patients. The value of plasma glucosylsphingosine in biochemical confirmation of the diagnosis of NPC is discussed.

Gpnmb Is a Potential Marker for the Visceral Pathology in Niemann-Pick Type C Disease

Impaired function of NPC1 or NPC2 lysosomal proteins leads to the intracellular accumulation of unesterified cholesterol, the primary defect underlying Niemann-Pick type C (NPC) disease. In addition, glycosphingolipids (GSLs) accumulate in lysosomes as well. Intralysosomal lipid accumulation triggers the activation of a set of genes, including potential biomarkers. Transcript levels of Gpnmb have been shown to be elevated in various tissues of an NPC mouse model. We speculated that Gpnmb could serve as a marker for visceral lipid accumulation in NPC disease. We report that Gpnmb expression is increased at protein level in macrophages in the viscera of Npc1nih/nih mice. Interestingly, soluble Gpnmb was also found to be increased in murine and NPC patient plasma. Exposure of RAW264.7 macrophages to the NPC-phenotype-inducing drug U18666A also upregulated Gpnmb expression. Inhibition of GSL synthesis with the glucosylceramide synthase (GCS) inhibitor N-butyl-1-deoxynojirimycin prevented U18666A-induced Gpnmb induction and secretion. In summary, we show that Gpnmb is upregulated in NPC mice and patients, most likely due to GSL accumulation.